BAROMETRIC PROGNOSTICS. 



21. Different meteorological observers have attempted to 

 embody and generalise the results of their observations in a 

 collection of rules, by which the weather may be prognosticated. 

 The following brief general maxims have been proposed : 



1. Generally the rising of the mercury indicates the approach of 

 fair weather, the falling of it shows the approach of foul weather. 



2. In sultry weather, the fall of the mercury indicates coming 

 thunder. In winter the rise of the mercury indicates frost. In 

 frost, its fall indicates thaw, and its rise indicates snow. 



3. Whatever change of weather suddenly follows a change in 

 the barometer, may be expected to last but a short time. Thus, 

 if fair weather follow immediately the rise of the mercury, there 

 will be very little of it; and, in the same way, if foul weather 

 follow the fall of the mercury, it will last but a short time. 



4. If fair weather continue for several days, during which the 

 mercury continually falls, a long succession of foul weather will 

 probably ensue ; and again, if foul weather continue for several 

 days while the mercury continually rises, a long succession of fair 

 weather will probably succeed. 



5. A fluctuating and unsettled state in the mercurial column 

 indicates changeable weather. 



Here is another set of weather barometric prognostics : 



1. If the barometer begin to fall slowly and steadily after a long 

 continuance of dry weather, rain will certainly follow ; but if the- 

 fair weather have been of very long duration, no perceptible change 

 may take place for some days, and the longer the time which 

 elapses between the fall of the barometer and the commencement 

 of the rain, the longer will be the subsequent continuance of the 

 foul weather. 



2. The preceding rule may be inverted. If the barometer 

 begin to rise slowly and steadily, after a long continuance of rainy 

 weather, fair weather will certainly follow ; and if several days 

 elapse between the rise of the barometer and its commencement, 

 it will have so much the longer continuance. 



3. If, in either of these cases, the changes follow promptly upon 

 the motion of the mercury, the new state of the weather will not 

 be of long continuance. 



4. If, during two or three days successively, the barometer rise 

 slowly and steadily, rain nevertheless falling constantly, fair 

 weather will certainly follow, and vice versd. But if the baro- 

 meter rise during rain, and then fall at the commencement of. 

 fair weather, the fair weather will be very transient ; and vice versd. 



5. A sudden fall of the mercury in spring or autumn is followed 

 by high winds ; in summer, and especially during sultry weather, 

 it is followed by a thunder-storm. In winter, a sudden fall after 



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